Series electric lamp



Aug. 23, 1960 H. A. BREEDING ETAL SERIES ELECTRIC LAMP 2 Sheets-Shea?. 1

Filed Aug'. 8, 1958 mnu-fllt d Statesv Patent C SERIES ELECTRIC LAlVIPHarold A. Breeding, Hendersonville, N.C., and Ernest C. Martt, ChagrinFalls, Ohio, assignors `to General Electric Company, a corporation ofNew York Filed Aug. s, 195s, ser. No. 754,057

s claims. (c1. 315-75) This invention relates to electric lamps intendedfor series service, and particularly to high pressure mercury vapordischarge lamps having an arc tube mounted in a vitreous outer envelopeor jacket and adapted for such service. More specifically, the inventionrelates to an integral arcing fuse or short circuiting featureassociated with the leads of the lamp for continuing an electric circuittherethrough in case of failure of the lamp.

The operation of electric lamps in series for such services as streetlighting provides a substantial reduction in the cost of wiring.Moreover, in the case of discharge lamps, the need for individualballast transformers, normally required by reason of the negativeresistance characteristics of these lamps in order to limit the currenttherethrough, is eliminated. The single transformer or control devicewhich regulates the current through the series string performs theentire function.

When lamps are operated in series, it is necessary to provide some meansfor preventing the extinguishment or improper operation of the remaininglamps in the series upon failure of any one lamp. Otherwise, the highopen circuit voltage of the entire series string is developed at thefailed lamp and causes an arc therein or across its socket and may ruinthe socket. Such means may take the form of cutouts which short circuitany faulty lamps, for instance upon failure of the filament in the caseof an incandescent lamp. A type of cutout commonly used for this purposecomprises a disc of copper coated with an oxide film mounted betweenaluminum discs serving as contacting electrodes. One cutout arrangementused with mercury vapor lamps comprises a pair of the `above cutoutsplaced back-to-back connected across the socket terminals in parallelwith the lamp. The oxide films 4break down when the lamp fails to startand causes a short :circuit of the socket, thus allowing the circuit tocontinue operating with the remaining lamps.

We have found that copper oxide cutouts frequently fail to operateproperly. In general they are not satisfactory for use with mercuryvapor discharge lamps. A cutout may fail even though the lamp is stillsatisfactory for service and the cutout appeared satisfactory prior tofailure. A cutout failure requires that the utility send out a truckcrew to change the cutout, a relatively expensive operation.

The principal object of the invention is to provide a new and improvedelectric lamp having an arcing fuse device asociated with its leads forcontinuing an electric circuit therethrough in case of lamp failure.

A more specific object of the invention is to provide an arcing fusearrangement in the base of a discharge lamp which will not be subject tothe faulty or erratic operation encountered with lm cutouts. Also, anarrangement is desired which will short circuit a faulty lamp before itssocket has become damaged by the excessive heat developed by arcing.

We have found that the faulty and erratic operation of lm cutouts whenused with discharge lamps is due to the non-conformity of the breakdowncharacteristics of the Patented Aug. 23, i969 oxide lms by comparisonwith the breakdown characteristics of the lamps under high voltagepulses. When straight series circuits are switched on, or when lightningstrikes the line, high voltage pulses of short time duration may becreated. These pulses or switching transients may rise to severalthousand volts in a matter` of l to 100 microseconds and then decay tolower values and eX- tinguish. When the rise time of a pulse isprogressively shortened below 100 microseconds, the breakdown voltage ofthe discharge lamp rises. The copper oxide disc cutouts are not affectedin an identical manner and their breakdown voltage does not increase tonearly the same extent when the rise time is shortened. As a result, thebreakdown voltage of a lamp which is lower than that of the film cutoutin the absence of switching transients, becomes higher than that of thecutout when subjected to pulses of suihciently short time duration.

According to the invention we have found a solution to this problemwhich eliminates the use of film cutouts entirely, Instead, an integralarcing fuse is provided which requires the ionization of a gaseousmedium. This type of fuse has been found to have a breakdown voltagewhich increases as the rise time of high voltage pulses applied theretois shortened. As a result, the arcing fuse arrangement may be designedto have a breakdown voltage which is higher than that of the lamp underall conditions, even in the presence of high voltage pulses of Veryshort rise time or duration.

In accordance with the invention, a convenient and economical integralarcing fuse arrangement is provided within the base of an electric lampby passing one of the leadin wires emerging from the stem of theenvelope through a vitreous sleeve around which one or more turns of theother lead-in wire are wrapped. In order for the fuse to operatereliably, it is necessary that a high lead content glass be used for thesleeve to assure that the lead-in wires become welded or solderedtogether in a low resistance juncture. We have also determined thatstout inlead wires of substantial size are necessary in order to haveenough metal at the juncture to elfect a good Weld. In a preferredconstruction of a mercury vapor discharge lamp embodying the invention,one inlead is passed through an insulating lead glass sleeve which ispositioned for the most part Within the stem tube of the outer envelopeor jacket and laid alongside the exhaust tube thereof, and the otherinlead wire is wrapped around both the insulating sleeve and the exhausttube.

For further objects and advantages and for a detailed description of theinvention, attention is now directed to the following description andaccompanying drawings illustrating a preferred embodiment of theinvention. The features believed to be novel will be more particularlypointed out in the appended claims.

ln the drawings:

Fig. 1 is a front elevation view of a high pressure mercury vapor lampembodying the invention with the front portion of the outer jacket andof the base cut away to expose the internal construction of the arcingfuse.

Fig. 2 is a sectional view through .the upper end of the lamp of Fig. l.

Fig. 3 is a diagrammatic view of several lamps embodying the inventionarranged in a series circuit.

Fig. 4 shows a cross sectional view of the base portion of a lampmounted in a socket and illustrates the appearance of a short circuitedarcing fuse.

Fig. 5 illustrates schematically a circuit which may be used fordetermining pulse breakdown characteristics.

Fig. 6 illustrates the measured characteristics of the pulse wave shape.

Fig. 7 is a graph illustrating the breakdown characteristics ofdischarge lamps and film cutouts, and also of arcing fuses in accordancewith the invention.

quartz about the electrode inleads.

Referring to the drawing. and more particularly to Fig. 1, there isshown a high pressure mercury vapor lamp 1 comprising an outer vitreousenvelope or jacket 2 of vgenerally tubular form modified by a centralbulbous portion 3. It is provided at its outer end with a reentrant stem4 having a press 5 through which extend relatively stitf inlead wires 6,7 providing connections from the arc tube to the contact surfaces of theusual screw-type base 8, namely the threaded shell 9 and the insulatedcenter contact 11.

The inner arc tube 12 is made of quartz or more properly fused silica,and has sealed therein at opposite ends a pair of main dischargesupporting electrodes 13, 14 plus an auxiliary starting electrode 1S atthe base end. The electrodes have inleads 16, 17 and 18 respectively,each including an intermediate thin foil section 19 hermetically sealedthrough full diameter pinch seals 21, 22 at the ends of the arc tube.Main electrodes 13, 14 each comprise a tungstenV wire helix 23 wrappedaround the core portion and a small elongated piece of thorium metal(not shown in the drawing) inserted between the core and the helix.Auxiliary starting electrode 15 consists merely of the inwardlyprojecting end of inlead 18.

Inlead 16 to main electrode 13 enters pinch seal 21 through afunnel-like opening 24 and has a portion embedded in the quartz which isbent over at right angles and welded 4to the foil section. 'Its outerend is welded to the bent over portion of stem lead-in wire 7. Inlead 17of main electrode 14 is connected by a exible wire 'to transverselydirected portion 26 of single support rod 27 which serves as a currentconductor to inlead 6. Inlead 18 of auxiliary electrode 15 iselectrically connected tolead-in wire 6 by a resistor 28 welded thereto.

Fulldiameter pinch seal 21, 22 may be made by flattening or compressingthe ends of the arc tube without prior necking down to a smallerdiameter according to copending application No. 607,005, tiled August30, 1956, of Klaus Gottschalk, entitled Quartz Tube Pinch Seal andassigned to the same assignee as the present invention. The arc tube isprovided with a supply of mercury in suicient quantity to be completelyvaporized with a pressure of the order of one-half to severalatmospheres during operation of the lamp. In addition a small quantityof a rare gas such as argon at a low pressure, for instance atapproximately 25 millimeters pressure, is provided to facilitatestarting.

The'principal support of the arc tube is provided by longitudinallyextending side rod 27 whose base end is welded to the laterally bentover portion of lead-in Wire 6. A transverse spring member 29 fastenedto the lower end of the support rod bears against the lower tubularportion of the jacket to brace the support rod. A pair of similar springmembers 30, 31 fastened on either side Vof transverse portion 26 bearagainst the outer tubular por-tion of the jacket and xes the outer endof the support rod in place. The arc tube is clamped to the support rodby a pair of metal straps 32, 32 Wrapped around the pinch seals andwelded to support rod 27. The straps are spaced a distance away from theends of the arc chamber in order to prevent devitriiication of theTransverse ridges 33, 33 lformed across the faces of the pinch seals andengaged by Vthe inner edges of the straps prevent axial movement of theVarc tube. Y

In accordance with the invention, an arcin-g fuse is provided in Contactwith the outside air within stem tube 4 of the jacket and enclosedofcourse Within base 8. Lead-in Wires 6, 7 of the outer envelope orjacket each comprise solid wire inner portions 6a, 7a, intermediatedumet portions 6b, 7b and externalV stranded portions o Componentmaterial:

4 portions 6b, 7b consist Yof copper-sheathed iron Wire for eliecting ahermetic seal where they pass through the press. External strandedportions 6c, 7c have a relatively large total cross section but arestranded to achieve the desired exibility. v

The lead-in wires enter the stern tube through the press on either sideof centrally located exhaust tube 35. One of the lead-in wires, 7c asillustrated in Fig. l, passes through a slender thin-walled glass sleeve36 whose inner end is buttedY against the press of the stern and whichextends substantially the entire length of the stem tube. The glasssleeve is laid alongside exhaust tube 35 and external stranded portion6c of lead-in wire 6 is wrapped one or more turns around both theexhaust tube and the glass sleeve. This arrangement is the mostconvenient to manufacture. As illustrated, lead-in wire portion 6c iswrapped two turns around the exhaust tube and glass sleeve and is weldedto locking ring 37 which is engaged by the base shell 9. Externalstranded portion 7c is soldered to the center contact or eyelet 11 ofthe base.

We have found that glass sleeve 36 must be made of a highVV lead contentglass which will not bubble when melted, for instance a glass containingapproximately 20% or more lead oxide by weight. This is necessary inorder for the arcing fuse to operate reliably and achieve a lowresistance weld or juncture between stranded portions 6c, 7c in theregion of the wrap around loops. While dissolved in the glass as aconstituent, the lead is in the form of lead oxide and transparent;during arcing a black color appears indicating the presence of leadmetal. This lead metal helps to weld or solder the contacts together andassures a low-resistance joint as a result of which the assembly coolsalmost to the ambient temperature. Actual tests of such welded juncturesusing high lead content glass have indicated a cold resistance less than0.1 ohm. On the other hand if lime glass is used for the sleeve, theassembly often remains red hot as long as current is flowing and theresistance when cold measures as an open circuit. Y

In a preferred embodiment of a 40G-Watt lamp for operation at 3.2amperes Ywith a 13S-volt arc drop and providing approximately 20,000lumens in the horizontal burning-position, glass sleeve 36 wasapproximately 0.120 inch in diameter and 11/2 inches long with a wallthickness of approximately 0.024 inch. The high lead content glass used,sometimes known as 012 glass, has the following composition expressed inrange of percentages by weight.

YRange, percentage by weight Silica (SiOZ) 55-60 Lead oxide (PbO)27.0-31.0

Potassium oxide (KZO) 6.5-9.0 Sodium oxide (Na2O) 3.0-5.5 Alumina(A1203) 0.5-2.0

In the preferred embodiment illustrated in the drawing, not only glasssleeve 36 but also exhaust tube 3S and stem tube 4 are made of the highlead content glass specitied above. Inasmuch as the exhaust tube islikewise melted at least in part by the arc and tends to ilow in orabout the lead-in wire juncture, it is advantageous to have it likewisecontain a high percentage of lead.

The size of wire used for external stranded portions 6c and 7c is notcritical. However the Wire should be substantial enough so that therewill -be sufficient metal to form the desired weld or juncture. At thesame time, of course, the wire should not be so heavy in relation to thecurrent intended for the circuit in which the lamp is to operate thatthe heat formed by the arc will be conducted away too rapidly to 'allowthe metal to melt. In a 40G-watt lamp intended for a 3.2 lamperecircuit, a suitable wire for stranded portions 6c, 7c consists of 8strands of 12 mil nickel plated copper wire twisted around a single coreof 20 .mil nickel wire. vThis wire has a total cross sectionV of 1552circular 'mils (0.00114 sq. in.). By

comparison, wire having only 1056 circular mils was found insuicient.

As shown in Fig. 3, in the use of lamps in accordance with theinvention, a string of lamps 1a to lq are connected in series andenergized from an alternating source of constant current regulated to3.2 amperes applied to terminals 39. The lamps are mounted horizontallyin insulated sockets 41, as shown in Fig. 4, comprising a threaded shell42 and center contact 43.

If a lamp, 1b for example, fails as by rupture of one of the inleadsinto the arc tube, the full open circuit voltage of the source appearsacross that lamp. This may be several thousand volts and is suicient tocause `an arc to form between lead-in wire portions 6a, 7a in theinterenvelope space between the outer jacket and the arc tube whereinthe fill gas may be nitrogen at approxi mately 380 millimeters pressuremeasured at 25 C. The heat from the arc gradually causes the lead-inwires to melt back toward the stem and the arc then proceeds to burnthrough the press and likewise causes it to melt, as shown at 5' in Pig.4. At such time of course the jacket is aired but the arc continues toburn between the external stranded portions 6c, 7c of the lead-in wires.Surface tension causes the melted wire ends to ball up and increase indiameter. Finally the arc reaches glass sleeve 36 and begins to melt itback. At this time the proximity of the wrap-around turns in strandedportion 6c to stranded portion 7c permits a conductive juncture to beformed between the balled up ends, as indicated at 44. The formationofthe juncture is aided by the use of high lead content glass which doesnot bubble and blow away the molten metal. Also lead released from thehigh lead content glass may help to achieve a low resistance juncture;as a result, the arc is extinguished, the juncture cools and lamp 1b iseffectively short circuited. The remaining lamps in the string continueto operate in normal fashion while lamp 1b remains cool and its socket41 is not overheated nor damaged as would otherwise happen. Y

One of the most important advantages of the integral arcing fusearrangement of the invention is that it is not subject to the faultyoperation encountered with oxide lm cutouts. Referring to Fig. 5, thebreakdown characteristics of various components under short durationpulses were measured using a repetitive pulse generator 45. The outputthereof was applied at 46 to the lamp or cutout or arcing fuse whosecharacteristics are to be determined. A meter 47, which may include acathode ray oscilloscope and an electrostatic voltmeter, is connectedacross the terminals.

A typical pulse wave shape is -illustrated at 48 in Fig. 6. For a givenrise time to the peak, the peak volts were gradually increased until thepoint of ioniziation or breakdown was reached. This point was indicatedby a sudden drop-off of the voltage curve as illustrated at 48. rlibemaximum value of voltage or peak volts just reached when breakdownoccurred is that used in plotting the curves of Fig. 7.

Referring to Fig. 7, curves 5t), `5l and 52 illustrate the averagebreakdown voltage determined for three groups of copper oxide lm cutoutsof basically similar construction. These curves form a family havingsimilar characteristics. t will be noted that there is only a moderaterise in breakdown voltage as the rise time to ltlhe peak of the appliedpulse is shortened. For instance, referring to curve 51, the breakdownvoltage with `a pulse having a rise time of 10'() microseconds isapproximately 1900 volts, and for a rise time of one microsecond isapproximately 2200 volts.

Band curve 53 illustrates the average breakdown characteristics of40G-watt mercury vapor lamps such as that previously described. For arise time to the peak of 100 microseconds, the breakdown voltage isapproximately 600 volts. As the rise time is lengthened, for instance to4167 microseconds, corresponding to 1A of %0 second interval and beingthe rise time of the usual 60-cycle applied voltage, the breakdownvoltage decreases slowly, for instance to about 200 volts. However whenthe rise time is shortened below microseconds, the breakdown voltageclimbs rapidly and in the region from 1 to 10 microseconds crosses overthe breakdown voltage curves 50 to 52 of the film cutouts. In the'region under 1 microsecond, the breakdown vvoltage of the lamps isdefinitely yhigher than that of the cutouts. Thus in the range below l0microseconds, false cutout operation is apt to occur. In general,shifting the breakdown charaIteris-tic of the cutout upwards is notadequate to cure this condition. If the breakdown voltage of the cutoutis increased in Order to establish it above that of the lamp for pulsesof very short rise time, the breakdown voltage of the cutout will be sohigh relative to that of the lamp in the case of a 60-cycle appliedvoltage without pulses, or Iwith pulses of long rise time exceeding 100microseconds, that the cutout will no longer offer adequate protection.

The superior performance of the arcing fuse arrangement in accordancewith the invention is illustrated by curve 54. This curve has the samegeneral shape as band curve 53 and climbs with decreasing rise time inthe saine fashion. The probable explanation of this characteristic isthat initial breakdown voltage of the arcing fuse depends uponionization of the nitrogen filling gas in the inter-envelope space, aprocess essentially similar to the ionization of the `argon and mercuryvapor medium within the arc tube. The breakdown voltage of the arcingfuse as vindicated by curve 54 is throughout the entire range of risetime, located at a substantial voltage over that of the lamps. This ofcourse indicates that the lamp, providing its characteristics arenormal, will always break down rst and the arcing fuse will only breakdown wlhen the lamp has become defective.

The arcing fuse arrangement according to the invention is also suitablefor use with lament lamps, particularly filament lamps provided with agas filling such as nitrogen or argon wherein ionization may occur afterrupture of the filament. Whether used with discharge or incandescentlamps, the integral arcing fuse construction of the invention provides asimplication in installation and `a substantial overall cost saving byeliminating the need for separate cutouts.

While the invention has been described by reference to a specificpreferred embodiment in `a given size of mercury vapor discharge lamp,the same, including its details of construction, is intended asexamplary and not in order to limit the invention thereto except in sofar as included in the appended claims.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. An electric lamp having an integral arcing fuse and comprising avitreous envelope, a stem closing an end of said envelope and having `apair of lead-in wires projecting therethrough, a high lead content glasssleeve enclosing the external portion of one of said lead-in wirespassing through said stem, the external portion of the other of saidlead-in wires having at least one turn wrapped around said sleeve, and abase provided with contact surfaces attached to the stem end of saidenvelope and having the ends of said lead-in wires connected to itsContact surfaces.

2. An electric lamp having an integral arcing fuse and comprising avitreous envelope, a re-entrant stem closing an end of said envelope andhaving an exhaust tube passing centrally therethrough, a pair of lead-inwires passing through a press in the inner end of said stem, saidlead-in wires having external portions projecting through said stem tubeon either side of said exhaust tube, a high lead content glass sleevepositioned around one of said external lead-in portions within said stemtube, the other of said external lead-in portions having at least oneturn wrapped around both said vitreous sleeve and said exhaust tube, anda base provided with contact surfaces attached to the stem end ofv saidjacket and having the ends of said external lead-in `portions connectedto itscontact surfaces.

3. A lampras in claim 2 wherein said glass sleeve consists of glasscontaining at least approximately lead oxide by weight in order toassure a low resistance juncture between said external lead-in portionsin the region of said wrap around turn as a result of arcing betweensaid lead-in Wires upon failure of said lamp.

4.` An electric discharge lamp having an -arcing fuse and comprising avitreous outer jacket enclosing a generally cylindrical arc tubedeiining an arc chamber having electrodes sealed therein at oppositeends, a stem closing an end of said jacket and having a pair of lead-inwires projecting therethrough, a high lead content glass sleeveenclosing the external portion of one of said leadin wires passingthrough said stern, the external portion of the other of said lead-inwires having at least one turn wrapped around AsaidA sleeve, and a baseprovided with contact surfaces attached to the stem end of said jacketand having the ends of said lead-in wires connected to its contactsurfaces.

5. An electric discharge'lamp having an arcing fuse and comprising avitreous outer jacket enclosing a generally cylindrical arc tubedelining an arc chamber having electrodes sealed therein at appositeends, a re-entrant stem closing an end of said jacket and having anexhaust tube passing centrally therethrough, a pair of lead-in wirespassing through a press in the inner end of said stem and havingconnections to the electrodes of said arc tube, said lead-in wireshaving external portions projecting-through said stern tube on eitherside of said exhaust tube, a high lead content glass sleeve positionedaround one of said external lead-in portions Within said stem tube, theother of said external lead-in portions having at least one turn wrappedaround both said vitreous sleeve and said exhaust tube, and a baseprovided with contact surfaces attached to the stem end of said jacketand having the ends of said external lead-in portions connected -to itscontact surfaces.

6. An electric discharge lamp having an arcing fuse and comprising avitreous outer jacket enclosing a generally cylindrical arc tubedeningan arcV chamber containing a quantity of mercury and-an VstartingV gasand having electrodes Vsealed therein at opposite ends,` a reentrantstem closing an end-of said jacket andhaving an exhaust tube passingcentrally therethrough, a press in 'the inner end of said stem and apair of lead-in wires passing therethrough having connections to theelectrodes of said arc tube, a base comprising a threaded metal shelland insulated center contact fastened to the stem end of said jacket,said lead-in wires having stranded external portions projecting throughsaid stem tube on either side of said exhaust tube, a high lead contentglass sleeve positioned around one of said stranded lead-in portionswithin said stern tube, the other of said stranded lead-in portionshaving atleast one turn wrapped around both said vitreous sleeve andsaid exhaust tube, the ends of said stranded lead-in portions beingconnected one to said threaded metal shell land the other to saidinsulated center contact. Y Y

7. A lamp as in claim 6 wherein said glass sleeve consists of glasscontaining at least approximately' 20% lead oxide by weight in order toassure a low resistance juncture between said stranded lead-in portionsin the region of said wrap around turn as a result of arcing betweensaid lead-in wires upon failure of said lamp A 8. A lamp as in claim 6for operation at approximately 3.2 amperes wherein said glass sleeveconsists of glass containing at least approximately 20% lead oxide byWeight and has a Wall thickness of approximately 9.024 inch and saidstranded lead-in portions have cross sections of approximately 1550circular mills in order to assure the formation of a low resistancejuncture between said stranded lead-in portions in the region of saidwrap around turn as a result of arcing between said lead-in wires uponfailure of said lamp.

Johnson Nov. 2l, 189'3 Hierholzer June 10, 1958'

